Perturbation-based dual task assessment in older adults with mild cognitive impairment.

Background: Dual tasking (i.e., concurrent performance of motor and cognitive task) is significantly impaired in older adults with mild cognitive impairment (OAwMCI) compared to cognitively intact older adults (CIOA) and has been associated with increased fall risk. Dual task studies have primarily examined volitionally driven events, and the effects of mild cognitive impairment on reactive balance control (i.e., the ability to recover from unexpected balance threats) are unexplored. We examined the effect of cognitive tasks on reactive balance control in OAwMCI compared to CIOA. Methods: Adults >55 years were included and completed the Montreal Cognitive Assessment (MoCA) to categorize them as OAwMCI (MoCA: 18-24, n = 15) or CIOA (MoCA: ≥25, n = 15). Both OAwMCI [MoCA: 22.4 (2.2), 65.4 (6.1) years, 3 females] and CIOA [MoCA: 28.4 (1.3), 68.2 (5.5) years, 10 females] responded to large magnitude stance slip-like perturbations alone (single task) and while performing perceptual cognitive tasks targeting the visuomotor domain (target and tracking game). In these tasks, participants rotated their head horizontally to control a motion mouse and catch a falling target (target game) or track a moving object (track). Margin of stability (MOS) and fall outcome (harness load cell >30% body weight) were used to quantify reactive balance control. Cognitive performance was determined using performance error (target) and sum of errors (tracking). A 3 × 2 repeated measures ANOVA examined the effect of group and task on MOS, and generalized estimating equations (GEE) model was used to determine changes in fall outcome between groups and tasks. 2 × 2 repeated measures ANOVAs examined the effect of group and task on cognitive performance. Results: Compared to CIOA, OAwMCI exhibited significantly deteriorated MOS and greater number of falls during both single task and dual task (p < 0.05), and lower dual task tracking performance (p < 0.01). Compared to single task, both OAwMCI and CIOA exhibited significantly deteriorated perceptual cognitive performance during dual task (p < 0.05); however, no change in MOS or fall outcome between single task and dual task was observed. Conclusion: Cognitive impairment may diminish the ability to compensate and provide attentional resources demanded by sensory systems to integrate perturbation specific information, resulting in deteriorated ability to recover balance control among OAwMCI.

Functional electrical stimulation to enhance reactive balance among people with hemiparetic stroke.

BACKGROUND: Individuals with stroke demonstrate a twofold higher fall incidence compared to healthy counterparts, potentially associated with deficits in reactive balance control, which is crucial for regaining balance from unpredictable perturbations to the body. Moreover, people with higher stroke-related motor impairment exhibit greater falls and cannot recover balance during higher perturbation intensities. Thus, they might need supplemental agents for fall prevention or even to be included in a perturbation-based protocol. Functional electrical stimulation is a widely used clinical modality for improving gait performance; however, it remains unknown whether it can enhance or interfere with reactive balance control. METHODS: We recruited twelve ambulatory participants with hemiparetic stroke (61.48 ± 6.77 years) and moderate-to-high motor impairment (Chedoke-McMaster Stroke Leg Assessment ≤ 4/7). Each participant experienced 4 unpredicted paretic gait-slips, with and without functional electrical stimulation (provided 50-500 ms after perturbation) in random order. The paretic quadriceps muscle group was chosen to receive electrical stimulation, considering the role of support limb knee extensors for preventing limb-collapse. Outcomes including primary (laboratory falls), secondary (reactive stability, vertical limb support) and tertiary (compensatory step length, step initiation, execution time) measures were compared between the two conditions. RESULTS: Participants demonstrated fewer falls, higher reactive stability, and higher vertical limb support (p < 0.05) following gait-slips with functional electrical stimulation compared to those without. This was accompanied by reduced step initiation time and a longer compensatory step (p < 0.05). CONCLUSION: The application of functional electrical stimulation to paretic quadriceps following gait-slips reduced laboratory fall incidence with enhanced reactive balance outcomes among people with higher stroke-related motor impairment. Our results lay the preliminary groundwork for understanding the instantaneous neuromodulatory effect of functional electrical stimulation in preventing gait-slip falls, future studies could test its therapeutic effect on reactive balance. Clinical registry number: NCT04957355.

Age-related differences in reactive balance control and fall-risk in people with chronic stroke.

BACKGROUND: Impaired reactive responses to sudden environmental perturbations contribute to heightened fall-risk in healthy aging and neurologically impaired populations. Previous studies have demonstrated individual contributions of paretic and non-paretic sides to fall-risk in people with stroke with variable levels of motor impairment. However, the combined effect of aging and unilateral cortical lesion on reactive balance control is not clearly understood. We therefore aimed to examine age-related differences in reactive balance control and fall-risk during laboratory-induced gait-slips in people with comparable stroke-related motor impairments. METHODS: Thirteen younger (45.61 ± 4.61 years) and thirteen older (71.92 ± 6.50 years) adults with similar stroke-related impairment (on Fugl-Meyer Lower Extremity Assessment) were exposed to one overground gait-slip under each limb (paretic and non-paretic). Center of mass state stability and slipping kinematics (slip displacement and velocity) were computed. Clinical balance and mobility were also assessed. RESULTS: On non-paretic slips, older adults with chronic stroke demonstrated greater falls and lower center of mass stability (its position and velocity) at post-slip touchdown compared to younger adults with chronic stroke (p < 0.01). This was accompanied with a greater peak slip displacement and faster peak slip velocity (p < 0.01). However, there were no such group differences noted on the paretic slips (p > 0.01). CONCLUSION: Aging may have an independent, detrimental effect on reactive balance control in people with chronic stroke. Non-paretic deficits in controlling slip intensities (slip displacement and velocity) can accentuate fall-risk in older adults with chronic stroke. Further investigation is necessary to identify additional factors attributing to heightened fall-risk in older adults with chronic stroke.

Mobile Brain Imaging to Examine Task-Related Cortical Correlates of Reactive Balance: A Systematic Review.

This systematic review examined available findings on spatial and temporal characteristics of cortical activity in response to unpredicted mechanical perturbations. Secondly, this review investigated associations between cortical activity and behavioral/biomechanical measures. Databases were searched from 1980-2021 and a total of 35 cross-sectional studies (31 EEG and 4 fNIRS) were included. Majority of EEG studies assessed perturbation-evoked potentials (PEPs), whereas other studies assessed changes in cortical frequencies. Further, fNIRS studies assessed hemodynamic changes. The PEP-N1, commonly identified at sensorimotor areas, was most examined and was influenced by context prediction, perturbation magnitude, motor adaptation and age. Other PEPs were identified at frontal, parietal and sensorimotor areas and were influenced by task position. Further, changes in cortical frequencies were observed at prefrontal, sensorimotor and parietal areas and were influenced by task difficulty. Lastly, hemodynamic changes were observed at prefrontal and frontal areas and were influenced by task prediction. Limited studies reported associations between cortical and behavioral outcomes. This review provided evidence regarding the involvement of cerebral cortex for sensory processing of unpredicted perturbations, error-detection of expected versus actual postural state, and planning and execution of compensatory stepping responses. There is still limited evidence examining cortical activity during reactive balance tasks in populations with high fall-risk.

Assessing Skin Blood Flow and Interface Pressure in Patients With Spinal Cord Injury Provided an Alternating Pressure Overlay: A Cross-sectional Study

The effects of an alternating pressure (AP) overlay on the skin are not fully understood. PURPOSE: This study was conducted among persons with spinal cord injury (SCI) to examine skin blood flow (SBF) and interface pressure (IP) during and after AP overlay use. METHODS: In this cross-sectional, repeated measures study, persons eligible for participation were clinic outpatients from a large metropolitan area in the midwest United States who were 18 to 65 years old with a SCI with a neurologic level of injury at T10 or above for more than 1 year and used a wheelchair for primary mobility. Persons with a current pressure injury, diabetes mellitus, and/or hypertension or other vascular or pulmonary diseases were excluded. Data regarding age, gender, body mass index (BMI), duration of SCI, and American Spinal Injury Association Impairment Scale scores were collected. The experimental study involved 3 protocols: the AP protocol (participants lay supine for 40 minutes on an operating room [OR] pad with a low-profile AP that used a 10-minute inflation-deflation cycle); the post-AP protocol (participants lay on the 2-inch foam OR pad for 40 minutes), with 30 minutes of rest in between; and the control protocol, comprised of 40-minutes of laying supine on the OR pad. Each participant served as his/her own control. Outcome variables included 1) peak IP (the highest value among adjoining sensors located at the highest pressure point); 2) averaged IP (the averaged value of the sensors), calculated from pressure mapping system data from the sacrum and left heel; and SBF, measured using a laser Doppler flowmetry system. Descriptive analyses were performed for all variables to determine need for parametric or nonparametric analyses. The mean value of peak IP, averaged IP among inflation and deflation cycles of AP, and post-AP and control protocols were compared using repeated measures analysis of variance (ANOVA). Mean SBF among inflation and deflation cycles of AP and post-AP and control protocols were compared using the nonparametric Friedman test, and Wilcoxon signed rank tests were used to compare the SBF responses during the post-loading period. If the results of repeated measures ANOVA or Friedman tests were statistically significant, paired t tests and Wilcoxon signed rank tests were used for pairwise comparison with Bonferroni correction at alpha level 0.0125, respectively. RESULTS: Among the 15 participants (11 men, 4 women; age 41.77 ± 14.49 [range 20-62] years; BMI 26.81 ± 4.13 [range 22-37]; injury duration 17 ± 14.62 [range 1-48] years; mostly (11) African American), peak IP decreased during the AP deflation at sacrum (51.47 ± 30.18 mm Hg vs. 114.13 ± 60.97 mm Hg; P = .002) and heel (26.79 ± 12.91 mm Hg vs. 53.05 ± 18.22 mm Hg; P = 0 .001), and SBF increased at the heel (27.92 ± 32.15 vs. 10.43 ± 11.16 au; P = .006) but was not significant at the sacrum (15.54 ± 15.33 au vs. 11.96 ± 10.26 au, P = .023). Peak IP decreased during post-AP at the sacrum (104.62 ± 58.17 mm Hg; P = .002) but not at the heel (47.69 ± 16.21 mm Hg; P = .097). SBF increased during post-AP at the sacrum (15.78 ± 15.82 au; P = .012) but not at the heel (16.31 ± 29.18 au, P = .427). CONCLUSION: An AP overlay redistributed IP and increased SBF at the sacrum and heel during use, and its effect 40 minutes after removal was observed only at the sacrum. Studies, including evaluating the lasting effect of AP on weight-bearing tissue protection at different anatomical locations, are needed.